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LIBRO DE ACTAS (pdf) - Universidad de Sevilla

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Melodic Transcription of Flamenco Singing from Monophonic and Polyphonic Music Recordings<br />

1.3 Automatic transcription of sung melodies<br />

Automatic transcription is one of the main research challenges in the field of sound and music<br />

computing. It consists in computing a symbolic musical representation (in terms of Western<br />

notation) from a given musical performance (Klapuri, 2006). For monophonic music material,<br />

the obtained transcription relates to the melody (Gómez et al., 2003) and in polyphonic music<br />

material there is an interest in transcribing the predominant melodic line (Klapuri, 2006).<br />

Transcription systems can provi<strong>de</strong> melodic <strong>de</strong>scriptors at different levels. The main melodyrelated<br />

Low-level features are energy, associated with loudness, and fundamental frequency (f0)<br />

related to its perceptual correlate, pitch. From now on, we will use the term pitch to refer to f0.<br />

In a higher structural level, audio streams are segmented into notes, and their duration and pitch<br />

provi<strong>de</strong> a symbolic representation. This representation can be the input to higher-level music<br />

analyses, e.g. ornament <strong>de</strong>tection, melodic contour extraction or key or scale analysis. Current<br />

systems for automatic transcription are usually composed of three different stages: low-level<br />

(frame-based) <strong>de</strong>scriptor extraction, note segmentation and note labelling.<br />

When <strong>de</strong>aling with monophonic music signals, existing transcription systems provi<strong>de</strong><br />

satisfying results for a great number of musical instruments. Although we find some successful<br />

approaches for singing voice (Mul<strong>de</strong>r et al. 2003; Ryynänen, 2006), it is still one of the most<br />

complex instruments to transcribe, even in a monophonic context. This is due to several factors,<br />

such as the continuous character of the human voice and the variety of pitch ranges and timbre.<br />

This results in difficulties in obtaining correct f0 estimations, <strong>de</strong>tecting note transitions and<br />

labelling notes in terms of pitch or duration. When <strong>de</strong>aling with polyphonic music signals,<br />

current state-of-the-art algorithms for predominant f0 estimation yield an overall accuracy<br />

around 75% according to the 2011 edition of the Music Information Retrieval Evaluation<br />

eXchange (MIREX). Moreover, audio onset <strong>de</strong>tection methods yield an average F-measure<br />

around 0.78 (MIREX). This F-measure is obtained for a mixed dataset of 85 files, but if we just<br />

consi<strong>de</strong>r the 5 tested singing voice excerpts, the maximum F-measure is 0.47. In addition,<br />

current approaches are oriented towards mainstream popular music. This leads us to the<br />

question of how would these algorithms perform for, e.g. traditional music, and more<br />

particularly, flamenco singing. Additional challenges in flamenco transcription arise from the<br />

quality of existing recordings, the acoustic and expressive particularities of singing, its ornamental<br />

and improvisational character and the yet to be formalized musical structures employed (Mora et<br />

al., 2010).<br />

2. Selected approach<br />

Figure 1 shows an overall diagram of the proposed system, which is based on the one<br />

<strong>de</strong>scribed in (Janer et al., 2008). It consists of four main steps: low-level feature extraction<br />

(fundamental frequency, energy and spectral features), tuning frequency estimation, transcription<br />

into short notes, and an iterative process involving note consolidation and refinement of the<br />

tuning frequency.<br />

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